Question

what is wavefront.

Answer 1

in one dimension.. we talk about crests and troughs
but in two or three dimensions.. these crests and troughs take a shape.. so that shape is called the wave front..

Answer 2

what is the physical significance of wave front

Answer 3

well.. looking at a wave front you can understand what sort of source Created it..

for example.. if its a point source.. you get circular ripples in water.. which m pretty sure you have seen.
so if by chance you see perfect circular ripples.. you bet .. that the source was a point source..